Arrangement for adjusting width of fibre web

ABSTRACT

An arrangement for adjusting the width of a fibre web in an apparatus comprising two filter wires permeable to water, the filter wires having the same direction of travel, and a conduit for placing pulp suspension between the wires. The arrangement comprises channel for feeding water between the wires and to the edges thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an arrangement for adjusting the width of afibre web when water is removed from pulp suspension in an apparatuscomprising two filter wires permeable to water, the filter wires havingthe same direction of travel and both wires being arranged to besupported by surfaces equipped with water openings and to formtherebetween a gap narrowing in the direction of travel, and side partslocated on both edges of the gap to prevent the pulp suspension frombeing extruded out of the gap in the crosswise direction thereof, theopenings in the upper and lower surfaces of the gap being formed suchthat the both surfaces comprise a solid edge part next to the side partssuch that the edges of the wires extend over said solid edge parts, andmeans for feeding the pulp suspension into the gap between the wires inthe inlet direction thereof.

2. Description of Related Art

When water is removed from pulp suspension when, for example, ash orother impurities are washed off it, the pulp is usually fed to agap-like space confined by wires. Behind the wires, there are supportingsurfaces equipped with holes or other openings, whereby the water can beremoved via the wires and further via the openings thereof. It is alsoknown that openings cannot be used in the supporting structure at theedges of the wires running in the gap but the supporting structure musthave a solid section at the edge part of the gap in order to prevent thepulp from penetrating under the edges of the wire. On the sides of sucha gap there are also provided side plates to close the gap such that thepulp suspension is not extruded out of the gap to the sides thereof butproceeds towards the outlet opening of the gap in the direction oftravel of the wire. The gap is shaped so as to narrow in the directionof flow of the pulp suspension such that the pulp suspension is pressedagainst the wires; consequently, the water flows through the wire. Theproblem with such an apparatus is that the pulp suspension tends tobecome pressed to the edges of the wire and further under the edgesthereof, thereby dirtying the edges of the wires and, furthermore, thepulp suspension splatters all over at the outlet opening of the gap,dirtying the apparatus. In order to prevent the above, it is known touse water jets to wash the pulp off the edge of the wire and thus toprevent the edge of the wire from becoming dirty and the pulp from beingsplattered all over. This solution is, however, rather difficult sinceusing water jets necessarily causes splashes and it is difficult tocollect the water and the fibre material removed by the water jets.

Attempts have also been made to utilise various sealing elements toblock the gap between the wires so that the pulp suspension cannot beextruded from the edge. The problem with this solution is that the wiresequipped with seals are extremely expensive and, furthermore, theirservice life is quite short. The use of separate seals, in turn, hasproved to be difficult in practice since the pulp suspension penetratesextremely easily between the wires and the seals before the actualsealing is performed. Controlling the separate seals has also proved tobe difficult, and the seals tend to wear quickly.

SUMMARY OF THE INVENTION

An object of the invention is to provide a solution by which thedisadvantages of the known solutions are avoided and which is easy toimplement. An arrangement of the invention is characterized in that thearrangement comprises means for feeding water to the sides of the gapsuch that while flowing together with the pulp suspension towards theoutlet opening of the gap, the supplied water pushes the pulp suspensiontowards the centre of the gap at least substantially as far as to theopenings in the upper and lower surfaces.

The basic idea of the invention is that such an amount of water is fedinto the gap to the sides thereof that the water is pressed towards thecentre of the gap as the height of the gap decreases, the watersimultaneously pushing the pulp suspension away from the edge of thegap, whereby the web that exits from the chamber between the two wiresis narrower than the wires, the edge of the wire becoming substantiallypurified of pulp. The advantage of the invention is that an extremelysmall amount of water can push the pulp from the edge of the gap towardsthe centre thereof. The supplied water, which retains its volume,penetrates towards the centre of the gap as the height of the gapdecreases, simultaneously narrowing the web until the openings in thesupporting structure on the other side of the wires allow excess waterto be removed from the gap; consequently, the pulp remains on the wiresubstantially along the entire width between the extreme openings. Thewater not only pushes the pulp from the edge of the gap towards thecentre thereof but also washes the edges of the wire substantiallyclean, thereby substantially preventing splashing at the outlet end ofthe gap or the apparatus from becoming dirty. The feeding of water inaccordance with the invention is also extremely easy to implement byplacing only one or more water feeding hoses or channels in the sideplates of the gap, for example; no other separate equipment isnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in closer detail in the accompanyingdrawings, in which

FIG. 1 is a schematic side view of an apparatus of the invention,

FIG. 2 is a schematic cross-sectional view of the apparatus of FIG. 1taken along line A—A indicated in FIG. 1, and

FIG. 3 is a schematic sectional view of the apparatus of FIG. 1 takenalong line B—B indicated in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a schematic view of an apparatus of the invention, whereinwater is removed from pulp suspension in order to wash particle-likeimpurities, such as ash, off the pulp suspension or in order toconcentrate the pulp suspension. The apparatus comprises a gap 1narrowing in the vertical direction. Upper and lower wires 2 and 3travel along the upper and lower surfaces of the gap, respectively. Thepulp suspension is fed between the wires 2 and 3 at the higher end ofthe gap 1. The pulp suspension flows in the direction of travel of thewires 2, 3 towards the lower end of the gap. Simultaneously, water isremoved from the pulp suspension through the wires 2, 3 and further viaopenings in upper and lower surfaces 4, 5 external to the wires tocollecting chambers 6 wherefrom the water and the impurities removedtherewith are discharged. The pulp suspension can be fed into the gap inany manner known per se.

On both sides of the gap there are sides shown in FIGS. 2 and 3 toprevent the pulp suspension from being extruded out from the sides ofthe gap, and, consequently, the pulp suspension is forced to flow onwardwith the wires 2, 3 while the water is removed through the wires, thepulp suspension remaining therebetween. Furthermore, the figureschematically shows control rolls 7 and 8 of the wires 2, 3 travellingthrough the gap, and a turning roll 9 around which the wires rotate toreturn to the higher end of the gap.

FIG. 2 is a schematic cross-sectional view of the gap of the apparatusin accordance with FIG. 1 taken along line A—A indicated in FIG. 1. Ascan be seen from the figure, the upper and lower wires 2 and 3 travelagainst the upper and lower surfaces of the gap, respectively, such thatspace is left therebetween for the pulp suspension. The upper and lowersurfaces 4, 5 of the gap 1 are perforated or otherwise equipped withsuitable openings 4 a, 5 a such that water is allowed to flowtherethrough. Furthermore, the edges of the gap comprise solid sectionswithout openings, i.e. edge parts 10. The edges of the wires 2, 3 extendover the edge parts such that water cannot be removed through the upperand lower surfaces at the edges of the wires. The figure also shows how,according to an embodiment of the invention, water feeding channels 13travel through side parts 11 and 12 of the gap to the side parts of thegap 1 such that water can be fed into the gap via the channels. Thefigure also shows how an amount of water appropriately fed has causedpulp suspension 14 to penetrate towards the centre of the gap,substantially only water remaining on the edges of the gap. When wateris fed into the gap 1 before the outlet opening at the lower endthereof, the supplied water 15 flows together with the pulp suspension14 towards the outlet opening. Since water is substantiallyincompressible, it must penetrate from the edge towards the centre ofthe gap as the height of the gap decreases. Consequently, the watersimultaneously pushes the pulp suspension towards the centre of the gapuntil the point where the water reaches the openings 4 a, 5 a of theupper and lower surfaces of the gap. As the height further decreasesfrom this point onward towards the outlet opening of the gap, the wateris, however, pressed towards the centre of the gap but is allowed toflow out through the openings 4 a, 5 a in the upper and lower surfaces4, 5, whereby the edge of the pulp suspension substantially sets at theopenings simultaneously with water being removed from the pulpsuspension through the wires and the openings in the surfaces. Thisfeature is illustrated in closer detail in FIG. 3. The figure furtherschematically shows how water can be fed directly from the sides andthrough the upper and lower surfaces of the gap to the solid sections 10without openings located in the edges of the surfaces. This isillustrated by arrows 13 a and 13 b. The feeding of water can then beimplemented by only supplying through the cover, by only supplyingthrough the edges or by combining these different feeding alternativesin an appropriate manner.

FIG. 3 is a schematic sectional view of the apparatus of the inventiontaken along line B—B indicated in FIG. 1. As can be seen in the figure,the pulp suspension covers the gap along the entire width thereof at thefeed end of the pulp suspension, i.e. at the higher end of the gap. Thefigure shows the water feeding channels 13. There can only be one waterfeeding channel at a suitable distance from the outlet opening of thegap or there can be several ones along the side of the gap. When wateris fed from the water feeding channels 13 to the edges of the gap 1, thewater 15 sets between the pulp suspension 14 and the side parts 11 and12 of the gap 1. As the height decreases, the water 14 penetratestowards the centre of the gap 1 until the openings 4 a and 5 a of theupper and lower surfaces 4 and 5 allow excess water to flow out, thewidth of the pulp suspension remaining substantially constant. If it isto be ensured that the edge of the pulp suspension is as well-defined aspossible simultaneously with the edge of the wire remaining as clean aspossible, more water can be fed at a shorter distance from the outletopening of the gap such that there is always a sufficiency of water atthe edges of the gap. The figure further illustrates how water can befed in the direction of flow of the pulp suspension at the inlet end ofthe gap at the same time when the pulp is, for example, appropriatelyfed directly from behind of the gap or from the upper or lower directionto the inlet end. This is illustrated by arrows 13 c denoting waterfeeding channels connected to the points in question. Also this mannerof feeding water can be used alone, together with water feeding takingplace from the sides, together with the manner of feeding water from theupper and lower surfaces to the solid edge part thereof, or separately,according to the circumstances.

The water supplied to the edges of the gap can either be fresh water orfiltrate water removed from the pulp containing a small amount of solidmatter, such as fines, etc., since the water does not need be completelypure here. Furthermore, the amounts of water fed can vary depending onthe situation, but quite small amounts of water suffice to yield thepresent desired result. The water feeding channels can either beseparate water feeding hoses or fixed channels etc. formed in the sidesof the gap. Furthermore, the edges of the upper and lower surfaces ofthe gap must comprise a solid edge sector of some width in order toprevent the pulp suspension from penetrating under the edges of thewires and to keep it between the wires by feeding water.

What is claimed is:
 1. An arrangement for adjusting the width of a fibreweb when water is removed from pulp suspension in an apparatuscomprising two filter wires permeable to water, the filter wires havingthe same direction of travel and both wires being arranged to besupported by surfaces equipped with water openings and to formtherebetween a gap narrowing in the direction of travel, and side partslocated on both edges of the gap to prevent the pulp suspension frombeing extruded out of the gap in the crosswise direction thereof,openings in the upper and lower surfaces of the gap being formed suchthat the two surfaces comprise a solid edge part next to the side partssuch that the edges of the wires extend over said solid edge parts, andmeans for feeding the pulp suspension into the gap between the wires inthe inlet direction thereof, wherein the arrangement comprises means forfeeding water into the gap to the sides thereof such that while flowingtogether with the pulp suspension towards the outlet opening of the gap,the supplied water pushes the pulp suspension towards the centre of thegap at least substantially as far as to the openings in the upper andlower surfaces.
 2. An arrangement as claimed in claim 1, wherein themeans for feeding water comprise water feeding channels connected to theside parts of the gap, via which channels water is fed to the edges ofthe gap via the sides of the gap.
 3. An arrangement as claimed in claim1, wherein the means for feeding water comprise channels for feedingwater from the upper and/or lower surface to the solid edge parts ofsaid surface.
 4. An arrangement as claimed in claim 1, wherein the meansfor feeding water comprise channels for feeding water into the gapsimultaneously with the pulp suspension to the inlet side of the gap. 5.An arrangement as claimed in claim 1, wherein the arrangement comprisesseveral channels for feeding water to both edges of the gap.
 6. Anarrangement as claimed in claim 1, wherein the means for feeding watercomprise means for feeding fresh water.
 7. An arrangement as claimed inclaim 1, wherein the means for feeding water comprise means for feedingfiltrate water separated from the pulp suspension.